The present invention relates to devices for obtaining and retrieving a sample of material for analysis. More particularly, the present invention relates to sampling devices which detach and retrieve a portion of the surface of a material for analysis of surface features and of the underlying material, such as, for example, of the inner portions of pipes found in electric generating "power" plants.
It is often necessary to test or examine material which has been subjected to a somewhat hostile operating environment. In order to accurately, quantitatively, determine the properties of a material, a sample must be obtained from the material for testing. Further, any detailed metallurgical examination requires a sample of material for laboratory analysis. The need for testing or examination of structural materials in remote locations can arise in a number of situations, including the interior of a pipe or conduit which transports material at temperatures and pressures which can cause changes in the mechanical properties of the material composing the pipe over its service life. Also, other equipment which is subjected to stress, and thermal, radiation, chemical, or other environmental conditions may need to be sampled and tested to determine the damaging effects caused by such conditions.
The effects of exposure to hostile environments, and mechanical and thermal stress can produce severe problems in many situations and with many types of equipment. Notably, an acute problem has developed in aging power plants which have been in service for long periods of time. The turbines which are utilized to generate power from steam are subjected to thermal, mechanical and corrosive stresses. These stresses can cause failure of all or part of a turbine. If no data is available as to the condition of the materials which compose the components of the turbine then an uninformed decision has to be made as to whether to continue to run the turbines without knowing their true condition; thus presenting the undesirable dilemma of either incurring a significant risk of failure or replacing, prematurely, the turbines prior to the expiration of their useful life. Continuing to run a turbine which has unknowingly become unreliable can, of course, result in catastrophic failure. In addition to the potential tragedy of human injury, there is the enormous expense, in such a situation of having to replace the entire turbine, simply because one component failed.
For the above reasons, at least, there is a great need for a means for determining the condition of the material components of turbines and similar mechanical structures which undergo stress over a prolonged period of time. There is in this respect, a great need to be able to predict the remaining useful life of these machines and their material components. Unfortunately, prior to the advent of the present invention, it was often not possible to accurately measure the present condition of materials subjected to long term stress without destroying or significantly deforming the material components of the mechanism to be tested or completely dissembling the mechanism to be inspected. Under certain prior art sampling techniques, for example, great expense and time was necessary to repair the damage done through the sampling process.
Many techniques have been developed in the prior art for obtaining a sample for analysis, in an attempt to mitigate the above problems. None has been truly successful in permitting sample removal from remote locations with minimal structural consequences. One technique, for example, makes two cuts into a surface to form a V-shaped groove in the piece of material to be tested. The cuts are made along the entire length of the material in order for the triangular shaped section of material to be removed from the main portion of the material. If the cuts are not along the entire length, two further cuts are needed at either end in order to release the triangular sample, or, the two cuts may be made by a slightly cupped grinding wheel, yielding a sample shape which is typically described as a "boat sample". These processes require a large sample to be taken from the underlying material, and each leaves a sharp hole which needs later repair. This repair of the underlying material is often time consuming and expensive and will generally result in a weakened structure. Further, performing such an operation remotely is not practical.
Another prior art technique which permits obtaining some information about the material while causing little or no damage to the component is referred to as "replication". In this technique, the surface of the material is replicated by application of a coating, generally after some mechanical polishing and chemical etching of the surface has been performed. The coating is applied in liquid form and allowed to harden and is then peeled off to reveal a mirror image of the surface features of the underlying material. This technique only allows for examination of surface features and does not allow for analysis of the underlying material. Also, it is typically not possible to perform this technique in remote locations. The lack of an actual, physical sample of the underlying material is obviously a significant drawback when attempting to evaluate the condition of certain power plant/turbine components.
As alluded to above, it is also possible to analyze underlying material structures by partial or complete dismantling of the mechanism involved. It may then be possible to examine or sample material components of the mechanism by conventional techniques, followed by replacement of the worn out or damaged parts and reassembly. This often necessitates lengthy shut down periods and requires a large amount of time and expense in the disassembly and reassembly of complicated machinery.
In view of the above, it is apparent that there exists a need in the art for a sampling device which at least overcomes the above-described problems.